1. Field of the Invention
The present invention relates to apparatus and process for the production of well fluids. More particularly, the present invention the relates to vertical trees that can be used in association with a horizontal Christmas tree for the production of oil and gas. Additionally, the present invention relates to the modification of horizontal Christmas trees so as to be adaptable for the receipt of a vertical tree.
2. Description of Related an Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
In petroleum and natural gas extraction, a “Christmas tree” is an assembly of valves, spools, and fitting used for an oil and gas well. Christmas trees are used on both surface and subsea wells. An example of subsea Christmas trees include conventional, dual bore, mono bore, through flowline, horizontal, mud line, mud line horizontal, side valve, and through-bore trees. The deepest installed Christmas tree is in the Gulf of Mexico at approximately 9,000 feet.
The primary function of a tree is to control the flow, usually oil or gas, out of the well. The tree may also be used to control the injection of gas or water into a non-producing well in order to production rate of oil from other wells. When the well and facilities are ready to produce and receive oil or gas, tree valves are open and the formation fluids are allowed to go through a flow line. This leads to a processing facility, storage depot and/or other pipeline eventually leading to a refinery or distribution center. Flow lines on subsea wells usually lead to a fixed or floating production platform or to a storage ship or barge.
A tree often provides numerous additional functions including chemical injection points, well intervention means, pressure relief means, monitoring points (such as pressure, temperature, corrosion, erosion, sand detection, flow rate, flow composition, valve and choke position feedback), and connection points for devices such as downhole pressure and temperature transducers. On producing wells, chemicals or alcohols or oil distillates may be injected to preclude production problems (such as blockages).
Functionality may be extended further by using the control system on a subsea tree to monitor, measure, and react to sensor outputs on the tree or even down the well bore. The control system attached to the tree controls the downhole safety valve while the tree acts as an attachment and conduit means of the control system to the downhole safety valve.
Tree complexity has increased over the last few decades. They are frequently manufactured from blocks of steel containing multiple valves rather than being assembled from individual flanged components. This is especially true in subsea applications where the resemblance to Christmas trees no longer exists given the frame and support systems into which the main valve block is integrated.
The Christmas tree is installed on top of the wellhead. A wellhead is used without a Christmas tree during drilling operations, and also for riser tie-back situations that later would have a tree installed at riser top.
Subsea trees have a large variety of valve configurations and combinations of manual and/or actuated hydraulic or pneumatic valves. A typical tree will have at least four or five valves. There are a pair of lower valves are called the master valves. Master valves are normally in the fully open position and are never opened or closed when the well is flowing so as to prevent erosion of the valve sealing surfaces. An actuated wing valve is normally used to shut in the well when flowing, thus preserving the master valves for positive shutoff for maintenance purposes. Hydraulically-operated wing valves are usually built to be failsafe closed, meaning they require active hydraulic pressure to stay open. This feature means that if control fluids fail, the well will automatically shut itself in without operator action. A valve at the top is called the swab valve and lies in the path used for well interventions, such as wirelines. For such operation, a lubricator is rigged up onto the top of the tree and the wire or coil is lowered through the lubricator, past the swab valve and into the well. Some trees have a second swab valve in which the valves are arranged one on top of the other.
Subsea trees are available in either vertical or horizontal configurations. Typically, a subsea tree would have a choke (permitting the control of flow), a flow line connection interface (such as a hub, a flange or other connection), a subsea control interface (direct hydraulic, electro hydraulic, or electric) and sensors for gathering data such as pressure, temperature, sand flow, erosion, multiphase flow, and single phase flow.
One type of Christmas tree has a pair of bores extending through it. One of bores is the production bore and the other is a tubing annulus access bore. In this type of wellhead assembly, the tubing hanger lands in the wellhead housing. The tubing hanger has two passages through it. One passage is the production passage and the other passage is an annulus passage that communicates with the tubing annulus surrounding the tubing. Access to the tubing annulus is necessary to circulate fluids down the production tubing and up through the tubing annulus, or vice versa, to either kill the well or circulate out heavy fluid during completion.
After the tubing hanger is installed and before the drilling riser is removed for installation of the tree, plugs are temporarily placed in the passages of the tubing hanger. The tree has isolation tubes that stab into engagement with the passages in the tubing hanger when the tree lands on the wellhead housing. This type of tree is normally run on a completion riser that has two strings of conduit. In a dual string completion riser, one string extends from the production passage of the tree to the surface vessel, while the other extends from the tubing annulus passage in the tree to the surface vessel.
Unfortunately, the need for the production of oil and gas has created shortages in the availability of such Christmas trees. Often, the well cannot be completed until such time as the Christmas tree is available. In certain circumstances, the Christmas trees may not be available for several years. In order to accommodate this problem, it is necessary for drillers to partially drill the well and then plug the well or cement the well so as to block the release of hydrocarbons from the well. The drilling rig can then be moved to another location.
Ultimately, when the Christmas tree is available for installation on the wellhead, the driller will move the drilling rig back to the location of the original hole, remove the plug, and begin to complete the drilling of the well. After the well is completed, the Christmas tree can be installed using the drilling risers.
Presently, the drilling rig can cost approximately one million dollars per day. As such, there is a great deal of waste of time and money during the time in which the Christmas tree is not available. The driller must rent the drilling rig in order to partially complete the well, wait for the Christmas tree, and then recall the drilling rig so as to complete the production process. Under certain circumstances, the driller may actually have the Christmas tree available, but must wait for the drilling rig to be available for the completion of the well. Ultimately, after the well is completed, the Christmas tree can be installed as needed.
Used horizontal Christmas trees are readily available. However, the refurbishment of such used horizontal Christmas trees is a very complex, time consuming and expensive tasks. Ultimately, the cost of refurbishing a used horizontal Christmas tree can be nearly equal to the cost associated with a new Christmas tree. During refurbishment, the wide variety of valves and controls must be completely modified so as to avoid problems associated with corrosion and erosion. Unless extensive modifications are made to these used Christmas trees, there can be a wide variety of leak paths which can occur if the used Christmas tree is utilized without refurbishment. As such, typically, refurbishment of horizontal Christmas tree is not an attractive alternative to producers.
In the past, various patents have issued relating to such Christmas trees and the plugs associated therewith. For example, U.S. Pat. No. 5,299,641, issued on Apr. 5, 1994 to Paulo et al., describes a Christmas tree for subsea production. The Christmas tree has a connector at a bottom thereof for the purposes of locking to the wellhead. A guide structure is provided having a central ring attached to the connector.
U.S. Pat. No. 7,596,996, issued on Oct. 6, 2009 to Zollo et al., provides a Christmas tree with an internally positioned flowmeter. This is a measurement device that has structure adapted to be removably coupled to the Christmas tree. A sleeve is operatively coupled to the structure. The flowmeter is positioned at least partially within the sleeve.
U.S. Patent Publication No. 2007/0034379, published on Feb. 15, 2007 to Fenton et al., provides a plug installation for deep water subsea wells. A plug retrieval and installation tool is used with a subsea well having a production tree, a tubing hanger, a passage that extends vertically through the tubing hanger, and the tree. A plug is located within a plug profile in the passage within the tubing hanger. The plug retrieval device has a housing and connector that is lowered on a lift line onto the upper end of the tree. An axially extendible stem in the housing is moved with hydraulic fluid controlled by an ROV into the production passage of the tubing hanger. An installation and retrieval member mounted to the stem engages the plug and pulls it upwardly in the passage while the stem is being moved upwardly and pushes the plug downward to install the plug while the stem is being moved downward.
U.S. Patent Publication No. 2009/0260829, published on Oct. 22, 2009 to D. J. Mathis, provides a subsea tree safety control system for limiting the probability of failure on demand of the tree. This subsea shut-in system serves to actuate a safety valve on the tree. The safety shut-in system includes a surface control station positioned above a water surface connected via an umbilical to a subsea control system positioned below the water surface to actuate the safety valve. The safety-in system is diagnostically tested without actuating the safety valve.
U.S. Patent Publication No. 20110036562, published on Feb. 17, 2011 to K. Braekke, discloses a well plug having a flexible expandable sealing and a metallic anchor that can be moved radially out or in by rotating a leadscrew in opposite directions. The well plug has a ball valve in a central longitudinal passage which is kept open whenever the leadscrew rotates. This increases the accuracy when setting the plug and reduces the risk of the plug moving uncontrolled in the well bore during setting or retrieval. The ball valve can be opened or closed by rotating a transmitting shaft within an angle of free motion before the leadscrew is pulled along in the rotation.
It is an object of the present invention to provide a production system wherein a vertical tree can be secured to a modified horizontal Christmas tree.
It is another object of the present invention to provide a production system that is able to effectively use used horizontal Christmas trees.
It is still another object of the present invention to provide a production system whereby used Christmas trees can be easily modified for use in conjunction with a vertical tree so as to be ready for use.
It is still another object of the present invention to provide a production system which effectively couples a vertical Christmas tree to a horizontal Christmas tree.
It is still another object of the present invention to provide a productions system whereby production can be expedited from an existing well.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.